ONDETRON-MD TAB

• Blocks 5-HT3 receptors in the gut and the chemoreceptor trigger zone, one of the most effective mechanisms for controlling vomiting.
• The mouth-dissolving formulation is absorbed without water, which matters when a patient cannot keep anything down.
• Highly effective in chemotherapy- and radiotherapy-induced nausea, where it transformed treatment tolerability.
• Useful in acute gastroenteritis in enabling oral rehydration to succeed, avoiding intravenous fluids.
• Causes no sedation and no extrapyramidal effects, unlike older antiemetics such as metoclopramide and prochlorperazine.

Not everyone gets these. Most are mild and settle as the course finishes.

• Ondansetron prolongs the QT interval. Contraindicated in congenital long QT syndrome, and use with caution in electrolyte disturbance, bradycardia and alongside other QT-prolonging drugs.
• Correct low potassium or magnesium before starting, particularly in a vomiting patient where both are likely.
• Contraindicated with apomorphine, which causes profound hypotension in combination.
• Risk of serotonin syndrome with SSRIs, SNRIs, tramadol and other serotonergic drugs.
• Antiemetics can mask the symptoms of a serious underlying cause. Persistent vomiting, particularly with abdominal pain, headache or fever, needs a diagnosis.
• Dose reduction is required in significant hepatic impairment.
• Handle the mouth-dissolving tablet with dry hands and place it on the tongue to dissolve — do not push it through the foil.
• Use in pregnancy only where clearly indicated, and in children only on paediatric advice.